Many electronic devices use consumer-replaceable batteries to power the device. Consumer-replaceable batteries are sold in standard sizes and voltages, with 1.5 volt, AA-sized zinc-manganese dioxide (i.e., alkaline) batteries being the most common primary battery. Other primary and secondary battery types found in the market today may take a variety of forms, from cylindrical (AA, AAA, C, D, etc.) to button or coin sized cells. The battery chemistry for such batteries is equally broad, including nickel-metal hydride, lithium-iron disulfide, lithium-manganese dioxide, zinc-air and carbon-zinc electrochemical systems, with the voltage for each dictated by the electrochemical reaction inherent thereto. Ultimately, most consumer-replaceable batteries output nominal, direct voltages of 1.5 or 3.0 volts. While some consumers prefer the reusability of secondary battery systems, primary battery systems usually provide superior performance characteristics. In any event, the foregoing demonstrates that consumer-replaceable batteries encompass a wide range of possibilities, and the International Electrotechnical Commission and the American National Standards Institute publish specifications for such batteries.
Devices powered by consumer-replaceable batteries include a wide range of different applications, although flashlights—and particularly flashlights utilizing at least one light emitting diode (“LED”)—are perhaps the most ubiquitous. Other devices designed to rely on consumer-replaceable batteries may include infra-red or radio remote controllers, cameras, electronic locking devices and wireless sensors (e.g., temperature probes, motion detectors, smoke detectors and the like).
Device manufacturers prefer consumer-replaceable batteries for their low cost, convenience and familiarity. In order to best leverage the advantages of these batteries, manufacturers will design the circuitry in their devices accordingly. For example, the battery compartment for a device may include multiple batteries provided in series to increase the total voltage delivered to the device. Additionally or alternatively, manufacturers may provide multiple batteries in series to improve the overall current delivered. The precise number and orientation of the batteries is dictated by the design intent and load requirements of the device.
Reliance upon consumer-replaceable batteries creates the possibility for improper insertion of the batteries, particularly when multiple batteries are present. Improper insertion usually involves the consumer installing the battery with the polarity reversed (i.e., rather than placing the negative terminal with the negative contact in the device, the positive terminal is, instead, positioned next to the negative contact or vice versa), although it may also encompass a battery simply not making proper electrical contact. As a result, the power delivered to the device may not be of the correct voltage or amperage, which could lead to damage to the circuitry and/or malfunctioning or non-functioning of the device itself.
Consequently, device manufacturers may include protection schemes to guard against improper battery insertion. Owing to extraneous components, these schemes often increase the cost of the device.
One protection scheme is a simple mechanical solution in which the batteries are inserted into a separate part, such as a cartridge. In this approach, the part is designed so that it is not physically possible for the consumer to improperly align the batteries within the cartridge and then fit the cartridge back into the device itself. Drawbacks to this approach include the added volume/space for receiving the cartridge and the fact that the cartridge is a separate component which can be misplaced and/or broken by the consumer.
Electronic protection schemes are also contemplated. For example, Schottky diodes have been employed, although these devices cause a large reduction of current that would negatively impact any device whose output is dependent on current. Additionally, Schottky diodes are relatively large in comparison to some of the other solutions discussed below.
FIG. 8A of U.S. Pat. No. 8,366,290 shows a schematic diagram of a reverse battery protection circuit. A p-channel metal-oxide-semiconductor field-effect transistor (“PMOS”) is connected between the internal voltage supply and the assembled circuit board of a flashlight. If a battery is installed in reverse order, no current will flow through the circuit to power the light emitting diode. In this protection scheme the device itself will not be powered if a battery is improperly installed. Also, subsequent circuitry is provided, in the form of a microcontroller and separate MOSFET driver, to operate the LED.
Another example of a charge, discharge and protection circuit is disclosed in U.S. Pat. No. 7,030,591. Here, a series of metal-oxide-semiconductor field-effect transistors (“MOSFETs”) are employed in a cascading fashion between the battery and the load. This arrangement of MOSFETs in series allows for selective, switchable charging and discharging of rechargeable batteries separately connected to the circuit.
A further example of a battery circuit for supplying power to an electronic device is found in U.S. Pat. No. 5,686,814. First and second auxiliary circuits prevent unwanted charging and reverse voltage from being applied to a parallel battery sources. Specifically, both auxiliary circuits include a MOSFET in combination with an op amp in order to effectively cut off power in the event one of the batteries is improperly installed. This arrangement is best classified as passive the microprocessor has no control over the protection MOSFET.